The present invention relates to a 2-stage fluidized bed fine iron ore reducing apparatus and a reducing method using the apparatus, for reducing a fine iron ore of a wide particle size distribution. More specifically, the present invention relates to a 2-stage fluidized bed fine iron ore reducing apparatus and a reducing method using the apparatus, in which a fine iron ore of a wide particle size distribution can be reduced in an economical and efficient manner, and impediment of the reducing gas flow due to the abnormal phenomena such as defluidizing and channeling can be effectively avoided during the operation.
In the conventional blast furnace method, the size of solid particles are very large, and therefore, the iron ore can be reduced within a fixed bed type furnace. However, in the case of a fine particle iron ore, if the gas velocity is low as in the fixed bed type furnace, low gas permeability and the sticking phenomenon occur, with the result that the operation may be halted. Therefore, a fluidized bed type method has to be necessarily adopted, so that the movements of solid particles can be made brisk with excellent gas permeability.
An example of the fluidized bed type furnace is disclosed in Japanese Utility Model Publication No. Sho-58-217615. This is illustrated in FIG. 1. As shown in FIG. 1, this furnace includes a cylindrical reducing furnace 91 and a cyclone 95. The reducing furnace 91 is provided with a raw iron ore feeding hole 92, a high temperature reducing gas injecting hole 93, and a reduced iron discharge hole 94. Further, in the lower portion of the reducing furnace, there is disposed a gas distributor 96. A reducing gas is supplied through the gas distributor 96, and a fine iron ore is supplied through the feeding hole 92. Then the reducing furnace is agitated, so that the fine iron ore and the reducing gas can be mixed so as for the iron ore to be reduced in a fluidized state. After the elapsing of a time period, if the fluidized bed rises up to the height of the discharge hole 94, then the reduced iron is discharged through the discharge hole 94. Here, the fluidized bed takes the form of a bubbling fluidized bed in which the reducing gas forms bubblings, and the bubblings grow while passing through the particle layer.
In the above described reducing furnace, however, in view of the productivity and economy, if the elutriation loss of the fine iron ore particles is to be diminished, if the gas consumption rate is to be minimized, and if the gas utilization degree is to be maximized, then the particle sizes of the raw iron ore particles have to be strictly limited. Accordingly, a fine iron ore having a wide particle size distribution cannot be handled. That is, the above described fluidized bed type furnace cannot treat an iron ore of a wide particle size distribution, but can use only 0-0.5 mm, 0.5-1 mm, 1-2 mm and the like. However, the actually available fine iron ore particles have a size of 8 mm or less. Therefore, if the naturally available fine iron ore is to be used, the fine iron ore has to be sorted by sieving, or it has to be crushed into the rated sizes. The result is that the productivity is lowered, and the production cost is increased, because it requires additional process steps and additional facilities.
In an effort to solve this problem, Korean Patent No. 117065 (1997) proposes a 3-stage fluidized bed type reducing apparatus having tapered furnaces as shown in FIG. 2. In this apparatus, a stable fluidizing of an iron ore of a wide particle size distribution is aimed at, and for this purpose, tapered furnaces are employed. Further, in order to improve the reduction rate and the gas utilization rate, first the iron ore is pre-heated, second pre-reduced and then finally reduced, thereby forming a 3-stage reducing process. That is, as shown in FIG. 2, an upper reaction vessel 10 pre-heats the iron ore in a bubbling fluidizing state. A middle reaction vessel 20 pre-reduces the iron ore in a bubbling fluidizing state. A lower reaction vessel 30 finally reduces the pre-reduced iron ore in a bubbling fluidizing state, thereby completing a continuous 3-stage fluidized bed type process.
In FIG. 2, reference codes 40, 50 and 60 indicate cyclones, reference code 70 indicates a hopper, and 80 indicates a melter-gasifier.
In this 3-stage tapered fluidized bed type reducing furnace, an iron ore of a wide particle size distribution can be stably fluidized, and the reduction degree and the gas utilization degree can be considerably improved, compared with the conventional single type cylindrical fluidized bed type furnace. However, this furnace employs 3 stages, and therefore, the facility cost is very high. Further, if a problem occurs in any one of the plurality of the reaction vessels, then other reaction vessels are affected, with the result that the total process is adversely affected. Thus if an abnormal phenomenon such as defluidizing or channelling occurs which is actually very frequent, then the fine iron ore particles drop through the holes of the gas distributor to be agglomerated at the bottom of the reaction chamber. Therefore, the gas flow is impeded, and this cannot be prevented.
The present invention is intended to overcome the above described disadvantages of the conventional techniques.
Therefore, it is an object of the present invention to provide a 2-stage fluidized bed fine iron ore reducing apparatus, and a reducing method using the apparatus, in which the degree of utilization of the reducing gas is increased, an iron ore of a wide particle size distribution can be reduced in an efficient and economical manner, and fine iron particles dropping through the holes of a gas distributor can be circulated back into the fluidized bed furnace, thereby preventing an impediment of the reducing gas flow due to abnormalities such as defluidizing or channeling.
In achieving the above object, the 2-stage fluidized bed type apparatus for drying, pre-heating and pre-reducing a fine iron ore in a first fluidized bed type furnace, and for finally reducing the fine iron ore (thus pre-reduced) in a second fluidized bed type furnace according to the present invention includes:
a first tapered fluidized bed type furnace for receiving a raw fine iron ore and a reducing gas to form a turbulent or bubbling fluidized bed so as to pre-heat and pre-reduce the raw iron ore;
a first cyclone for separating fine iron ore particles from a discharge gas of the first fluidized bed type furnace to recycle the separated fine iron ore particles into the first fluidized bed type furnace, the separated discharge gas of the first fluidized bed type furnace being discharged to external atmosphere;
a second fluidized bed type furnace for finally reducing the fine iron ore (thus pre-heated and pre-reduced) of the first fluidized bed type furnace, by forming a bubbling or turbulent fluidized bed by utilizing a discharge gas (reducing gas) of a melter-gasifier;
a second cyclone for separating fine iron ore particles from a discharge gas of the second fluidized bed type furnace to recycle the fine iron ore particles into the bottom of the second fluidized bed type furnace, the separated discharge gas of the second fluidized bed type furnace being supplied to the first fluidized bed type furnace as a reducing gas;
a first intermediate hopper positioned between the first and second fluidized bed type furnaces, for storing fine iron ore particles (dropped through the holes of a gas distributor of the first fluidized bed type furnace) to recycle them into the lower portion of the second fluidized bed type furnace; and
a second intermediate hopper positioned beneath the second fluidized bed type furnace, for storing fine iron ore particles (dropped through the holes of a gas distributor of the second fluidized bed type furnace) to recycle them into the lower portion of the second fluidized bed type furnace.
In another aspect of the present invention, the method for reducing a fine iron ore by using the above reducing apparatus according to the present invention is characterized in that: a first fluidized bed type furnace dries, pre-heats and pre-reduces the fine iron ore under a reducing atmosphere; a second fluidized bed type furnace finally reduces the pre-reduced fine iron ore; a hopper and a gas/solid particle sealing valve are installed beneath each of the fluidized bed type furnaces; and the fine iron ore particles dropping through the holes of the gas distributors during an abnormality of operation are circulated back into the fluidized bed type furnaces, whereby impediment of the gas flow is avoided.